1. Field of the Invention
The present invention relates to a glow plug control apparatus for controlling a glow plug so as to accelerate the ignition/combustion of a fuel by said glow plug or detect ions generated during the combustion of a fuel by said glow plug and a glow plug therefor.
2. Description of the Related Art
The recent trend is for more diesel engines having a high heat efficiency to be mounted on passenger cars for the purpose of enhancing fuel economy. Under these circumstances, the users have demanded further enhancement of fuel economy as well as further improvement of prevention of vibration or noise and actuation properties which are inferior to gasoline engine. On the other hand, from the standpoint of environmental protection, the exhaust gas has been demanded to be more clean.
In order to meet this demand, as disclosed in Japanese Patent Unexamined Publications No. Hei. 10-9113 and Hei. 10-77945, a feedback control has been proposed involving the use of results of detection of ions produced during the combustion of a fuel for the purpose of controlling the timing or amount of fuel injection in the engine. As a method of detecting ions there is particularly proposed a method involving the measurement of ionic current flowing due to the presence of ions produced by the application of a voltage across the glow plug and the inner wall of the combustion chamber of an engine.
Heretofore, a glow plug has played a role ranging from aiding actuation to stabilizing the engine drive until the completion of warming up and thus has normally not been energized after the completion of warming up. However, it has been made obvious that it is effective for the reduction of vibration or noise of the engine and purification of exhaust gas to energize the glow plug even after the warming-up of the engine so that the glow plug is kept at a relatively high temperature. A system has been proposed involving the energization of a glow plug depending on the operating conditions for the purpose of controlling the temperature of the glow plug to not lower than a predetermined temperature.
However, the above cited JP-A-10-9113 and JP-A-10-77945 merely disclose a system involving the energization of a glow plug before actuation (pre-glow period) and during the warming-up of the engine (after-glow period) and the use of the glow plug only for the detection of ionic current. In other words, the invention disclosed in the above cited patents cannot energize the glow plug even after the completion of warming-up to detect ionic current and control the engine. It is preferred that ionic current be detected to control the engine also in the stage before the completion of warming-up such as pre-glow period and after-glow period. However, when the system is arranged such that switching is made from the energization of the glow plug to the measurement of ionic current or vice versa during pre-glow period, particularly in the initial stage of energization of glow plug, it is likely that the temperature rise of the glow plug during pre-glow period can be delayed, deteriorating the actuation properties.
The present invention has been worked out in the light of the foregoing problems. An object of the present invention is to provide a glow plug control apparatus which can keep the temperature of the glow plug to not lower than a predetermined temperature even after the lapse of the stage after pre-glow period and the stage during the warming-up of an engine in addition to during these stages to lessen the vibration or noise of the engine and clean the exhaust gas and can detect ions produced during the combustion of a fuel to control the engine. Also, a glow plug suitable for the glow plug control apparatus and a method of detecting ions in the combustion chamber of an engine which has been warmed up are provided. Another object of the present invention is to provide a glow plug control apparatus which exhibits good actuation properties without deterring the temperature rise of the glow plug during pre-glow period.
To solve the foregoing problems, the present invention provide a glow plug control apparatus comprising a glow plug including a housing fixed to an engine, a heating element insulated from the housing which generates heat when energized by electric current supplied through two conductive paths at least either before or after the completion of warming-up of the engine and a ceramic heater having an exposed portion which is heated by the heating element and exposed to the interior of the combustion chamber of the engine; a glow plug energization controlling means for controlling the energization of the heating element of the glow plug depending on the surface temperature of the exposed portion so as to raise or keep the surface temperature to not lower than a predetermined temperature; an ion detecting means for detecting ions in the combustion chamber using the glow plug; a switching means for switching the state of the glow plug from the state of being controlled in energization by the glow plug controlling means to the state of being detected in ion by the ion detecting means or vice versa; and a switching command means for commanding the switching from the state of being controlled in energization to the state of being detected in ions by the switching means for a predetermined period of time from the time of injection of fuel into the combustion chamber when the surface temperature of the exposed portion is not lower than the predetermined temperature.
In accordance with the glow plug control apparatus of the invention, the glow plug energization controlling means controls such that the surface temperature of the exposed portion of the ceramic heater is raised or kept to not lower than a predetermined temperature. When the surface temperature of the exposed portion is not lower than the predetermined temperature, the switching command means commands the switching means to switch the state of being controlled in energization to the state of being detected in ions for a predetermined period of time from the time of injection of fuel.
For example, before the actuation of the engine, the glow plug is energized. The detection of ions is not conducted before the temperature thereof rises from a temperature as low as ordinary temperature to the predetermined temperature.
However, when the temperature of the glow plug reaches not lower than the predetermined temperature, the state of the glow plug is switched from the state of being controlled in energization to the state of being detected in ions for a predetermined period of time from the time of injection of a fuel into the combustion chamber. Accordingly, the detection of ions can be conducted in the internals of the rise of the temperature of the glow plug. Thus, engine control during actuation is made possible.
Thereafter, also in the stage of actuation and warming up of the engine, the surface temperature of the exposed portion of the glow plug is kept to the predetermined temperature at lowest, making it possible to detect ions. Accordingly, the engine control during warming-up can be conducted.
In accordance with the glow plug control apparatus, the surface temperature of the exposed portion of the glow plug is kept to the predetermined temperature at lowest even after the completion of warming-up. In this manner, the vibration and noise of the engine can be lessened and the exhaust gas can be cleaned. Further, ions produced by the combustion of the fuel can be detected, making it possible to control the engine.
The foregoing control may be conducted either before or after the completion of warming up of the engine. Accordingly, the foregoing control may be conducted at any time between pre-glow period before the actuation of the engine and after-glow period after the actuation of the engine and during the period after the completion of warming up.
Further, the foregoing control may be conducted at any time between before the actuation of the engine and before the completion of warming up. In this case, in the stage before the actuation of the engine, the detection of ions is not conducted before the temperature of the glow plug which has been energized reaches a predetermined temperature from a value as low as ordinary temperature. Therefore, the temperature of the glow plug can be raised without hindrance due to switching to the state of being detected in ionic current, giving favorable actuation properties. In this arrangement, similar control can be conducted even after the completion of warming up as mentioned above. Alternatively, control different from that made before the completion of warming up may be conducted after the completion of warming up.
Moreover, the foregoing control may be conducted at any time after the completion of warming up. In this case, after the completion of warming up, the surface temperature of the exposed portion of the glow plug can be not lower than the predetermined temperature. Therefore, the vibration and noise of the engine can be lessened and the exhaust gas can be cleaned. Further, ions produced by the combustion of the fuel can be detected, making it possible to control the engine.
Referring to the method of measuring the surface temperature of the exposed portion of the ceramic heater, a temperature sensor such as thermocouple may be embedded in the ceramic insulator. In this arrangement, the temperature of the exposed portion can be measured by means of such a temperature sensor such as thermocouple. Alternatively, since the resistivity of the heating element varies with temperature (normally rises as the temperature rises), the surface temperature of the exposed portion may be estimated from the resistivity of the heating element on the basis of previously determined relationship between the resistivity of the heating element and the surface temperature of the exposed portion.
The predetermined period of time from the time of injection of fuel commanded by the switching command means can be a predetermined value represented, e.g., by the crank angle from the time of injection of fuel. Further, the foregoing period of time from the time of injection of fuel is preferably selected depending on the load represented by the rotary speed of the engine, the opening of the accelerator, the position of the accelerator or the like. This is because the period of time during which ions can be detected to obtain data useful for engine control varies with the rotary speed of the engine or load.
The glow plug control apparatus may be arranged such that the foregoing predetermined temperature is selected from the range of from 500xc2x0 C. to 900xc2x0 C.
In the stage after the completion of warming up, when the glow plug is not energized, the surface temperature of the exposed portion of the glow plug varies with the rotary speed of the engine or the load conditions and thus falls within a range of from about 200xc2x0 C. to 900xc2x0 C. In other words, when the engine is rotated at a low speed under a low load, the surface temperature of the exposed portion of the glow plug may be lowered to about 200xc2x0 C.
It is known that even if the engine is rotated at a low speed under a low load to give a low combustion temperature, when the glow plug is kept at a certain high temperature, the ignition and combustion of the fuel can be conducted in a stabilized manner, making it possible to effectively clean the exhaust gas and prevent the vibration and noise. Accordingly, the predetermined temperature of the invention is selected from a range of from 500xc2x0 C. to 900xc2x0 C. In other words, the glow plug should be kept at a predetermined temperature selected from a range of 500xc2x0 C. to 900xc2x0 C.
Referring to the reason why the predetermined temperature is selected from a range of from 500xc2x0 C. to 900xc2x0 C., when the predetermined temperature falls below 500xc2x0 C., the resulting effect of stabilizing the ignition and combustion of the fuel in the engine is insufficient. On the contrary, when the predetermined temperature exceeds 900xc2x0 C., the glow plug is kept at a high temperature. In other words, when control is conducted such that the temperature of the glow plug is kept beyond 900xc2x0 C., the durability of the glow plug can be easily deteriorated. This is also because as the electric power consumed to energize the glow plug increases, the fuel economy lowers.
In the ceramic heater of the glow plug of the foregoing glow plug control apparatus, the heating element is covered by a ceramic substrate and the resistivity of the substrate between the heating element and the surface of the ceramic substrate is from 10 kxcexa9 to 1 gxcexa9 when the surface temperature of the exposed portion is from the predetermined temperature to 1,200xc2x0 C.
The heating element of the ceramic heater used in the glow plug control apparatus is covered by a ceramic substrate and thus cannot be subject to corrosion or oxidation due to combustion flame. Thus, the ceramic heater is allowed to generate heat in a stabilized manner or the detection of ions can be conducted in a stabilized manner.
In order that ions in the combustion chamber can be detected by applying a voltage across the heating element embedded in the ceramic substrate and the inner wall of the combustion chamber in the state of being detected in ions, the resistivity of the ceramic substrate interposed therebetween must be somewhat low.
In this respect, the glow plug to be used in the glow plug control apparatus of the invention is arranged such that the resistivity between the heating element and the ceramic substrate is from 10 kxcexa9 to 1 Gxcexa9 when the surface temperature of the exposed portion of the glow plug ranges from the predetermined temperature to 1,200xc2x0 C. In this arrangement, ions can be detected within this temperature range.
The reason why the surface temperature of the exposed portion of the glow plug should fall within a range of from the predetermined temperature to 1,200xc2x0 C. is that when the surface temperature of the exposed portion of the glow plug is not lower than the predetermined temperature, the state of the glow plug is switched to the state of being detected in ions for a predetermined period of time. Further, the surface temperature of the exposed portion of the glow plug may reach 1,200xc2x0 C. at highest in the initial stage of actuation of engine.
The reason why the resistivity of the substrate should fall within a range of from 10 kxcexa9 to 1 Gxcexa9 is that when the resistivity of the substrate is as extremely high as greater than 1 Gxcexa9, the resulting ionic current is so extremely small that it can difficultly be detected. Accordingly, the resistivity of the substrate is preferably 1 Gxcexa9 or less. On the contrary, when the resistivity of the ceramic substrate is too low, current flows through the ceramic substrate across the two ends of the heating element to cause defects such as migration. Accordingly, the resistivity of the substrate is preferably 10 kxcexa9 or more.
Another means for solving the foregoing problems is a glow plug control apparatus comprising a glow plug comprising a housing fixed to an engine, a heating element insulated from the housing which generates heat when energized by electric current supplied through two conductive paths at least either before or after the completion of warming-up of the engine and a ceramic heater having an exposed portion which is heated by the heating element and exposed to the interior of the combustion chamber of the engine; a glow plug energization controlling means for controlling the energization of the heating element of the glow plug depending on the resistivity of the heating element so as to raise or keep the resistivity to not lower than a predetermined resistivity; an ion detecting means for detecting ions in the combustion chamber using the glow plug; a switching means for switching the state of the glow plug from the state of being controlled in energization by the glow plug controlling means to the state of being detected in ions by the ion detecting means or vice versa; and a switching command means for commanding the switching from the state of being controlled in energization to the state of being detected in ions by the switching means for a predetermined period of time from the time of injection of fuel into the combustion chamber when the resistivity of the heating element is not lower than the predetermined resistivity.
There is often some relationship between the surface temperature of the exposed portion of the glow plug and the resistivity of the heating element. Instead of controlling by estimating the surface temperature of the exposed portion once from the resistivity of the heating element, similar control can be conducted by controlling the resistivity of the heating element within a range of not lower than a predetermined resistivity on the basis of the relationship.
In other words, in accordance with the foregoing glow plug control apparatus, the glow plug energization controlling means controls such that the resistivity of the heating element related to the surface temperature of the exposed portion of the ceramic heater is raised or kept to a predetermined resistivity or more. When the resistivity of the heating element is not lower than the predetermined resistivity, the switching command means commands that the switching means be switched from the state of being controlled in energization to the state of being detected in ions for a predetermined period of time from the time of injection of fuel.
Therefore, before the actuation of the engine, the glow plug is energized to raise the temperature thereof from a temperature as low as ordinary temperature to the predetermined temperature. In other words, the detection of ions is not conducted before the resistivity of the heating element reaches beyond the predetermined resistivity. However, when the temperature of the glow plug is not lower than the predetermined temperature, and the resistivity of the heating element thus reaches not lower than the predetermined resistivity, the state of the switching means is switched from the state of being controlled in energization to the state of being detected in ions for a predetermined period of time from the time of injection of fuel into the combustion chamber. Accordingly, the detection of ions can be conducted in the intervals of raising-up the temperature of the glow plug. Thus, engine control can be made also during actuation.
Further, in the subsequent stage of actuation and warming-up of engine, too, the resistivity of the heating element of the glow plug can be raised to a predetermined resistivity, that is, the surface temperature of the exposed portion can be raised to a predetermined temperature so that the detection of ions can be conducted. Accordingly, engine control can be made also during warming-up.
Moreover, even after the completion of warming-up, the resistivity of the heating element of the glow plug is raised to the predetermined resistivity, that is, the surface temperature of the exposed portion is raised to the predetermined temperature. In this manner, the vibration and noise of the engine can be lessened, and the exhaust gas can be cleaned. Further, ions produced by the combustion of the fuel can be detected, making it possible to control the engine.
The foregoing control may be conducted at least either before or after warming-up of the engine. Accordingly, the foregoing control may be conducted at any time between pre-glow period before the actuation of the engine and after-glow period after the actuation of the engine and during the period after the completion of warming up.
Further, the foregoing control may be conducted at any time between before the actuation of the engine and before the completion of warming up. In this case, in the stage before the actuation of the engine, the detection of ions is not conducted before the temperature of the glow plug which has been energized reaches a predetermined temperature from a value as low as ordinary temperature. Therefore, the temperature of the glow plug can be raised without hindrance due to switching to the state of being detected in ionic current, giving favorable actuation properties. In this arrangement, similar control can be conducted even after the completion of warming up as mentioned above. Alternatively, control different from that made before the completion of warming up may be conducted after the completion of warming up.
Moreover, the foregoing control may be conducted at any time after the completion of warming up. In this case, after the completion of warming up, the resistivity of the glow plug is not lower than the predetermined resistivity so that the surface temperature of the exposed portion can be raised to not less than the predetermined temperature. Therefore, the vibration and noise of the engine can be lessened and the exhaust gas can be cleaned. Further, ions produced by the combustion of the fuel can be detected, making it possible to control the engines
A further means for solving the foregoing problems is a glow plug having a housing, and an heating element insulated from the housing which generates heat when energized by electric current supplied through two conductive paths, characterized in that the heating element has a ceramic heater covered by a ceramic substrate and the resistivity of the substrate between the heating element and the surface of the ceramic substrate is from 10 kxcexa9 to 1 Gxcexa9 when the surface temperature of the forward end of the ceramic heater is from 500xc2x0 C. to 1,200xc2x0 C.
In the glow plug of the invention, the heating element is covered by a ceramic substrate and thus cannot be subject to corrosion or oxidation due to combustion flame. Thus, the ceramic heater is allowed to generate heat in a stabilized manner.
Further, in the glow plug of the invention, when the surface temperature of the forward end of the ceramic heater is from 500xc2x0 C. to 1,200xc2x0 C., the resistivity of the substrate between the heating element and the surface of the ceramic substrate is from 10 kxcexa9 to 1 Gxcexa9. In this arrangement, while the surface temperature of the ceramic substrate is kept to this range, the detection of ions can be conducted. Further, by keeping the surface temperature of the ceramic substrate to not lower than 500xc2x0 C., the ignition and combustion of fuel can be conducted in a stabilized manner, making it possible to lessen the vibration or noise of the engine and clean the exhaust gas.
A still further means for solving the problems is a method of detecting ions in the combustion chamber of an engine to which a glow plug is fixed, the glow plug comprising a housing, an heating element insulated from the housing which generates heat when energized by electric current supplied through two conductive paths and a ceramic heater having an exposed portion which is heated by the heating element and exposed to the interior of the combustion chamber. In the method, while the engine is being warmed up, the energization of the heating element of the glow plug is controlled depending on the resistivity of the heating element so as to raise or keep the resistivity to not lower than a predetermined resistivity and when the resistivity of the heating element is not lower than the predetermined resistivity, the state of the glow plug is switched from the state of being controlled in energization for a predetermined period of time from the time of injection of fuel into the combustion chamber during which period ions in the combustion chamber are detected.
In accordance with the method for detecting ions in the combustion chamber of an engine, energization is controlled in the stage of completion of warming-up of engine such that the resistivity of the heating element is raised or kept to not lower than a predetermined resistivity. In other words, energization is conducted to generate heat such that the surface temperature of the exposed portion of the ceramic heater reaches a predetermined temperature. Accordingly, even after the warming-up of the engine, the vibration or noise of the engine can be lessened and the exhaust gas can be cleaned.
Further, switching is made to the state of being controlled in energization, whereby the detection of ions in the combustion chamber is conducted using the glow plug. In this manner, ions produced during the combustion of fuel can be detected to help control the timing or amount of injection of fuel into the engine.
It may be arranged such that the detection of ions is conducted even while the warming-up of the engine is not completed yet.